Movable electrical contact carrier block for potentiometers



Feb. 27, 1968 R. 3. DE LONG ET AL 3,371,305

MOVABLE ELECTRICAL CONTACT CARRIER BLOCK FOR POTENTIOMETERS Filed Feb.21 1966 Rokert DeLong Robert Johnson Bud A. Paine INVENTORS 34m, mg. W

United States Patent C) MOVABLE ELECTRICAL CONTACT CARRIER BLOCK FORPOTENTIOMETERS Robert J. De Long, Temple City, Robert D. Johnson,

Pomona, and Bud A. Paine, Monterey Park, Calif., assignors to SpectrolElectronics Corporation, City of Industry, Calif., a corporation ofDelaware Filed Feb. 21, 1966, Ser. No. 528,925

2 Claims. (Cl. 338-202) ABSTRACT OF THE DISCLOSURE Disclosed is atrimmer type potentiometer having a resistance element and a lead screwdisposed in parallel relationship therein. A slide-r block engages thelead screw and moves in such a manner to carry electrical contact alongthe resistance element. The slider block is constructed of a moldedintegral unit having a flat base member with arms extending from onemajor phase thereof. The arms have inwardly directed ridges definingthreads thereon which engage the threads in the lead screw so as tocarry the slider block in the attached contacts along the resistanceelement. The arms are resiliently deformable in such a manner that theslider block can be snapped in ,place over the lead screw.

This invention relates generally to variable resistors and moreparticularly to lead screw actuated trimming potentiometers. Morespecifically, the present invention is directed to a unique constructionfor the movable electrical contact carrier block used in suchpotentiometers.

In the development of lead screw actuated trimming otentiometers, themovable electrical contact carrier blocks were first constructed byhaving a threaded opening longitudinally disposed through the sliderblock. The threaded adjusting shaft (lead screw) was threaded throughthis opening to obtain desired voltage ratio or resistance adjustment.It was very quickly found, however, that at the terminus of travel ateach end of the internal housing formed by the potentiometer housing themovable electrical contact carrier block exerted extreme force upon thehousing as the lead screw was turned, thus causing the housing torupture leaving the potentiometer non-adjustable.

As a result of the foregoing problem, the next stage of development ofsuch carrier blocks was to utilize a wire spring as a part of thecarrier block. This wire spring was used as the portion of the contactcarrier block which engaged the threads of the lead screw to cause thedesired movement. The wire spring was designed in such a manner that atthe terminus of travel of the carrier block the wire spring wouldratchet or ride over the threads of the lead screw. Although such aconstruction operated quite well for the purpose intended, i.e., toeliminate the force exerted by the slider block at each end of itstravel, the construction sometimes introduced backlash into the contactelement thus causing difiiculty during adjustment, and furthermorecreated some additional assembly problems. It is thought that thebacklash resulted from the minimal contact between the wire and thethreads of the lead screw thus causing the carrier block to be somewhatunstable.

An attempt was also made to eliminate each of the problems abovereferred to by going to a resilient plastic material which would gripthe threads upon the lead screw without having formed threads providedtherein, thus at the-terminus of travel causing the carrier block toslip before rupturing the housing. It was however found that such aconstruction did not operate satisfactorily.

Accordingly, it is an object of the present invention to provide a leadscrew actuated trimmer potentiometer including a movable electricalcontact carrier block having multiple thread engagement with the leadscrew and which ratchets or idles at each end limit position or terminuswithin the housing.

It is another object of the present invention to provide a lead screwactuated trimmer potentiometer including a movable electrical contactcarrier block which is readily assembled with the lead screw byspringing a side of the carrier block as it is placed upon the leadscrew, yet which eliminates backlash and thereby gives a positive travelin each direction to the electrical contact fingers which engage theresistance element within the potentiometer.

It is another object of the present invention to provide a lead screwactuated trimmer potentiometer including an electrical contact elementcarrier block which is extremely simple in configuration, is easy andinexpensive to manufacture and assemble, yet which is rugged andprovides positive electrical contact element travel under the mostadverse operating conditions.

Other and more specific objects and advantagesof the,

present invention both as to its method of operation and itsorganization will become apparent from a consideration of the followingdescription taken in conjunction with the accompanying drawing which ispresented by way of example only and is not intended as a limitationupon the scope of the claims appended hereto and in which:

FIGURE 1 is a perspective view partially cut away illustrating anassembled lead screw actuated potentiometer embodying an electricalcontact element carrier block constructed in accordance with the presentinvention;

FIGURE 2 is a perspective view, partially cut away, illustrating some ofthe features of an electrical contact element carrier block constructedin accordance with the present invention;

FIGURE 3 is a bottom perspective view of the electrical contact elementcarrier block in accordance with the present invention;

FIGURE 4 is a view similar to FIGURE 3 but having the electrical contactelement affixed in place;

FIGURES 5 and 6 are end views of an electrical contact carrier blockconstructed in accordance with the present invention in place upon thelead screw and illustrating the two extreme positions of the carrierblock during adjustment of the resistance of the potentiometer; and

FIGURE 7 is an end elevational view of a modified form of carrier blockconstructed in accordance with the present invention.

An electrical contact carrier block constructed in accordance with thepresent invention is adapted for use in a potentiometer having a leadscrew and a resistance element disposed in parallel positions within ahousing. The carrier block is constructed of electrically non-conductivematerial and includes a base member having the contact element afiixedto and extending from one side thereof and a pair of resilientlydeformable arm members aifixed to and extending from the other sidethereof. The two arm members extend around the lead screw more than butless than 360 and have opposed threaded surfaces which engage the leadscrew threads. The two resiliently deformable arms, at each terminal endof travel of the carrier block, ride over the threads of the lead screwby springing outwardly and then return to a position such that thethreads on the arm members and the lead screw are in mated engagement.

Referring now to the drawing and more particularly to FIGURE 1 thereof,a potentiometer of the lead screw actuated type is shown generally at 10and includes a housing 11 having a resistance element 12 and a leadscrew 13 dis-posed in parallel longitudinal relationship within thehousing. An electrical return element or collector bar 14 is disposedupon the base 15 of the housing 11. The electrical contact element 16 ismounted upon a carrier block 17 the construction of which will be morefully described below. The lead screw 13 terminates in a slotted head 18for purposes of rotating the lead screw 13 to cause the carrier block 17to travel therealong. Such travel effects adjustment of thepotentiometer by moving the contact element fingers along the resistanceelement 12 and collector bar 14 as is well known in the art. An 0 ring19 is utilized to seal the interior of the potentiometer fromcontaminants that may be contained in the ambient atmosphere while a pinmember 20 is utilized to preclude longitudinal movement of the leadscrew 13 Within the housing 11.

The remainder of the detailed construction and operation of a lead screwactuated potentiometer is well known in the prior art and furtherexplanation thereof is not deemed necessary at this point. The presentinvention is primarily directed to the electrical contact carrier block17 illustrated in more detail in FIGURES 2 and 3, to which reference ishereby made.

As is shown, the carrier block includes a base member 21 having a firstmajor surface 22 and a second major surface 23. Extending from thesecond major surface 23 are 4 a pair of resiliently deformable armmembers 24 and 25 (the bulk of the arm member 25 being removed in FIG. 2for clarity of illustration). Preferably the base 21 and the resilientlydeformable arms 24 and 25 are formed of electrically non-conductivematerial such as fiberglass filled nylon or other plastic. On theinternal surface of each of the outwardly extending resilientlydeformable arms there is provided a row of threads 26 and 27respectively. As is illustrated, the threads are in opposed relationshipwith each other and face somewhat downwardly toward the second majorface 23 of the base member 21. It should also be noted that the row ofthreads 26 and 27 is in each instance formed upon an elongated ridge28-29 respectively having surfaces directed towards the second majorface (this relationship is more clearly seen in FIG. 5). It shouldbecome apparent at this point that when the carrier block is in positionupon the lead screw 13 of the potentiometer as illustrated in FIGURE 1,there are only 3 areas of contact therebetween. Such areas of contactare the threads 26 and 27 along the resilient arms 24 and 25respectively, and an area which is disposed intermediate and midwaybetween the arms 24 and 25 and which extends longitudinally along thesecond major face of the base member 21. Such 3 contact areas aredesignated at 30 and are clearly seen in FIGURES 2 and 5.

Extending outwardly from the first major face 22 of the base member 21(more clearly seen in FIG. 3) are 3 protrusions 31, 32 and 33. These 3protrusions cooperate with openings provided in the movable electricalcontact 16 to retain the contact 16 rigidly afiixed to the first majorface 22 and extending outwardly therefrom so that positive electricalcontact can be made to the resistance element and the collector bar asabove described. As is shown specifically and more particularly inFIGURE 4 the contact 16 is fitted upon the first major face 22 of thebase member 21 in such a manner that the protrusions 31 through 33extend through openings provided therein. The three protrusions 31through 33 are then deformed as by application of heat thereto torigidly affix the contact 16 in place. In this manner a pair ofelectrical contact fingers 34 are provided to engage each side of thecollector bar 14 as shown in FIGURE 1 while an additional electricalcontact finger 35 is provided to engage the resistance element 12 asshown in FIGURE 1.

Referring now more particularly to FIGURES 5 and 6, the operation of theelectrical contact carrier block is more clearly illustrated. As is seenin FIGURE 5 the resiliently deformable arms 24 and 25 have the threads26 and 27 respectively thereof in engagement with the threads on thelead screw 13 as shown at 30. The lead screw 13 is also in engagement ata tangent thereof with the area intermediate the arms 24 and 25 alongthe second major face 23 of the base 21. The arms 24 and 25 as shown inFIGURE 5 are in a position such that the threads 26-27 thereof are inmating engagement with the lead screw threads. In this position, thecontact herein is caused to move along the lead screw 13 as it isrotated at any point other than at each end limit position of travelthereof.

Assuming now that the carrier block 17 as shown in FIGURE 1 is at eitherend limit position of its travel along the lead scre 13 in such a mannerthat it is abutting the housing. Under these circumstances, if the leadscrew 13 is rotated the threads 26-27 on the resiliently deformable arms24-25 are caused to ride over the threads on the lead screw 13 until intheir maximum outward position the arms 24-25 are as illustrated inFIGURE 6. As the lead screw 13 is further rotated, the arms 24-25, dueto their being resiliently deformable, return to the position shown inFIGURE 5. This operation continues so long as the lead screw 13 isturned in the same direction. At each turn of the lead screw the arms24-25 reciprocate outwardly to the position of FIGURE 6 and then backinwardly to the position illustrated in FIGURE 5. Although no damage isbeing imparted to the potentiometer, electrical adjustment is not beingmade and rotation of the lead screw should be reversed.

A carrier block in accordance with the present invention may includeonly one resiliently deformable arm having threads thereon which engagethe threads of the lead screw. Such a carrier block is illustrated inFIGURE '7 to which reference is now made. As is therein shown, a basemember 41 has a first major face 42 to which an electrical contact isafiixed and extends outwardly therefrom as above described. A rigid arm43 extends upwardly from a second major face 44 of the base member 41. Aresiliently deformable arm 45 also extends upwardly from the secondmajor face 44 of the base 41 and is in opposed relationship to the rigidarm 43. Formed on an internal downwardly directed surface of the arm 45is a row of threads 46 which cooperatively engage the threads on thelead screw 13. When the carrier block as shown in FIG- URE 7 is at anend limit of travel, the arm 45 reciprocates as is indicated by thearrow 47 to cause the threads 46 to ride over the threads on the leadscrew 13,

There has thus been disclosed a carrier block for a movable electricalcontact for a lead screw actuated potentiometer which provides multiplethread engagement with a lead screw thereof and which rides over oridles at each end limit position thereof, yet which has no backlash,which is simple and inexpensive to manufacture and assemble and which isrugged of construction. Although the movable electrical contact carrierblock of the present invention has been disclosed and described in somedetail with respect to two separate embodiments thereof, such is notintended as a limitation upon the scope of the present invention as isdefined in the appended claims.

What is claimed is:

' 1. In a potentiometer having a parallel disposed resistance elementand threaded lead screw within a housing, an electrical contact carrierblock comprising:

an electrically non-conductive base member having first and second majorfaces;

an electrically conductive contact element affixed to and extending fromsaid first major face of said base member; and

a pair of resiliently deformable arm members formed of electricallynon-conductive material integrally with said base member and disposed inopposed relationship on said second major phase of said base member,said arm members extending around said lead screw more thanone-hundred-eighty degrees but less than three-hundred-sixty degrees,each of said arm members including an elongated ridge having a surfacethereon directed toward said second 5 6 major phase, said surface havingthreads formed References Cited thereon for engagement with said leadscrew. UNITED STATES PATENTS 2. A contact carrier block as defined inclaim 1 in n which said threads on said ridges and an area intermedi-218701392 1/1959 Boums et 338*202 X ate and midway between said armmembers on said sec- 5 2,873,337 2/1959 Beams et 338 180 0nd major faceand extending ldngitudinally therealong i are the only areas ofengagement between said carrier ROBERT SCHAEFER P'lmary block and saidlead screw. H. J. HOHAUSER, Assistant Examiner.

